Saw-tooth wave generator



Feb. 3, 1953 w. J. HOWARTH 2,627,576

SAW TOOTH WAVE GENERATOR Filed Feb. 1, 1949 1 ==/15 oz/m/r 5 21 19 SYNC INVENTOR Miller J flowarlh TORNEY Patented Feb. 3, 1953 SAW- TOOTH WAVE GENERATOR Walter J. Howarth, Trenton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 1, 1949, Serial No. 73,972

1 Claim. (G1. 250-36) This invention relates to recurring waveform generators and more particularly to linear sawtooth generators for cathode ray beam deflection circuits and the like.

The simplest form of saw-tooth wave generator takes the form of a circuit arrangement wherein a capacitive element is charged through a resistance element. A switch, preferably of the electronic type, is connected across the capacitive element to periodically and quickly discharge the capacitive element. The long sloping portion of the saw-tooth wave then occurs during the charging portion of the cycle while the short and steep portion of the saw-tooth wave occurs during the discharge portion of the cycle.

It immediately becomes apparent, however, that the charging or long slope of the saw-tooth wave is non-linear because the resistor causes the capacitor to charge exponentially, that is the current through the charging resistor does not remain at a constant level.

It has been heretofore proposed therefore to employ, instead of a resistor, a constant current device such as an electron discharge device of, for example, the pentode type which passes a substantially constant current over a large range of applied anode voltages.

The simple neon tube which has been employed as a means for discharging the capacitive element has heretofore been replaced by trigger circuits involving electron discharge devices. However, a practical generator trigger circuit capable of operating satisfactorily over a wide range of frequencies and other conditions may require the employment of several independent electron discharge devices.

When it is desired to reduce the number of electron discharge devices to economize, it is sometimes proposed to dispense with the constant current device employed for charging the capacitive element. In this latter arrangement, however, the loss of linearity becomes serious. It may also be possible to reduce the number of electron discharge paths or tubes by eliminating or reducing the number of tubes in the capacitive element discharge circuit. But such arrangements are inefficient even to the extent of failing at high frequencies.

According to this invention a circuit arrangement is provided employing only two electron discharge devices of the triode or pentode type which has substantially linear saw-tooth wave output characteristics. The circuit is also capable of operation over a wide frequency range.

One controllable electron discharge device is employed for charging a capacitor while a secz I 0nd electron discharge device not only discharges the capacitorbut also cuts off the current in the charging tube.

A primary object of this invention is to provide for the generation of linear saw-tooth waves.

Another object of this invention is to provide a circuit arrangement operable over a wide range of frequencies for generating linear saw-tooth waves.

Another object of this invention is to provide a simple saw-tooth wave generator of high efliciency.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying'drawing wherein there is illustrated, by circuit diagram, one form of this invention.

Turning in more detail to the drawing there is shown a first electron discharge device or tube I and a second electron discharge device or tube 3.

Although tubes I and 3 are shown as triodes they may take the form of pentodes and although they are shown schematically as separate tubes they may be contained in the same envelope without departing from the spirit of this invention.

An anode potential is applied to the anode of tube I through resistance 5.

A condenser I is connected between the oathode of the electron discharge device I and a point of fixed potential such as ground" 9. An output circuit is connected to the cathode of tube I.

The anode of tube 3 is connected to the con trol electrode of tube I and a resistance element I I is connected between the control electrode and cathode of tube I In the particular form of the invention shown in the drawing, a resistance I3 is placed in the cathode circuit of tube 3.

The control electrode of tube 3 is connected to the anode of tube I through a condenser IS. A grid leak type resistance I1 is connected to the control electrode of tube 3.

The synchronizing signal for timing the oscillator is applied to the control electrode of tube 3 through a coupling condenser I9 and a resistance 2 I The operation of the device shown in the drawing may best be understood if the circuit arrangement is compared to the basic saw-tooth wave generator referred to above and including a capacitive element which receives its charge through a resistor and wherein a switch is connected across the capacitive element to quickly discharge it periodically.

In the circuit arrangement shown, condenser I is the capacitive element, tube I is the charging resistance or constant current device. In this connection the operating potentials may be chosen so that the tube I is operating above the knee portion of its characteristic curve. That is, in the portion of its curve which is substantially constant current regardless of the applied voltage. As stated above in another form of this invention, tube I may be of the pentode variety.

Tube 3 then is employed as a discharge circuit.

Let it be assumed that the cathodes of both tubes are emitting and a B pluspotential is ap plied to the anode of tube I. Condenser T will charge-up due to the current flow through tube I. As the condenser I charges, the 'anod'e of tube I 4 D. C. voltage measurements (VTVM)? Anode (tube l) V 270 Anode (tube 3) V 260 Control electrode (tube I) V 260 Control electrode (tube 3) V 40 Cathode (tube I) V 260 Cathode (tube 3) V +2 Total current ma 1.5

Having thus described the invention, what is claimed is:-

A saw-tooth wave generator comprising in combination, firstland second electron discharge will rise in potential. After it has risen acertain amount, the control electrode of tube 3 becomes suficiently positive to cause tube 3 to become conductive.

It might be stated here, that due to grid "current in tube 3, condenser It has assumediacharge which 'prevents'tube 3 from becoming conductive until the anode potential-oi tubel rises to-Ia high plus value.

When tube-3 becomes conductive, condenser i discharges through-tube 3. The discharge current flowing through resistance ii provides a negative bias entrie -control electrode oiitube i so that tube ii'scut oii. Condenser i continues to discharge until the current through resistor i i "decreases-to the point to permit'tube Ito again conduct at which-timethe control electrode of tube 3 is driven in a? negative direction cutting off tube 3 which in turn reduces the negative bias values listed below, they are listed by way of example only. The particular tube types and circuit. constants shown are suitable foremploymerit-in a saw-tooth wave generator adaptable as a horizontal oscillator in television deflection circuits wherein the frequency is in the neighborhood of 15,000 cycles per second.

Electron discharge devices I' aniline; fisNT Resistance 5 ohms 50,000 Condenser i "mid" .025 Resistor I! ohms 150 Resistor i3 do 200 Condenser I5 mfd; .005 Resistor ii (variable)' megohms 2 Condenser; i9- "mid" .00025 Resistor 2i 'ohms 500,000

devices, each of said devices having a cathode, an anode and at'least one control electrode, an output condenser, said condenser being connected Jetween the cathode of said first discharge device and a point of fixed reference potential, a line resistor, a terminal adapted to be energized from a. source of operating potential, said resistor being "connected between said terminal and the anode of said first discharge device,-a fixed grid resistor, said grid resistor havingga relatively; low impedance whereby saw-tooth Waves are '-assured and being connected between the controlelectrade and cathode of-said firstdischarge device, a direct current connectionbetween the grid-oi said first-discharge device and the, anode of said second discharge device; a cathode; resistor, said cathode; resistor having a relatively low impedaneeand being connected between the cathode of said second discharge device and saidpoint of fixed reference potential, a variable-grid-resistor, said variable resistor having a relatively high impedance and being connected between the control electrode of-said second-dischargedevice' and said point of fixed reference potential, a coupling condenser, said coupling condenser being connected between the control electrode of saidsecond discharge device and the anode of said first discharge device, an input resistor, said input resistor having a relatively high impedance, an input condenser, said input condenser being adapted to be energizedfroma source of syn 'ehronizing signals, said input-resistor being connected between said input condenser and the control electrode of said second discharge device and means for connecting an output, "circuit across said output condenser.

WALTER J. Howaa'rn.

.nsrnnnncas CITED The'fcllowing references are of recordzin the Rieke Not 1.2, 1943 

